This invention relates to systems and processes for treatment of organic matter that may be waste such as sewage, sludge in municipal refuse and the like, biomass material such as plants and crop waste or other organic source matter that may be converted to biogas and other products. The new system and process is a two phase process that may control the acid forming organisms in an acid reactor and the methane forming mechanisms in a methane reactor to control the hydraulic retention time requirements of the process.
Anaerobic two phase digestion processes have been known in the industry for processing organic matter to produce methane gas and other products. The anaerobic digestion may be carried out in a single reactor or in a two stage reactor wherein both involve the two phase, acid forming and methane forming, method of processing the organic matter. The organic matter may be waste or nonwaste matter, but may normally be waste products. The waste products may be sewage, municipal refuse, food waste, biomass such as plants, crops, plant and crop wastes and the like, and industrial liquid and solids waste.
These anaerobic two phase digestion processes may have been limited in their use due to the long retention times required for the anaerobic organisms to grow and process the organic matter. For complete mix reactors, the process may be slow and expensive due to the need for large reactors to process economical amounts of organic matter given the time required for microorganisms to grow and digest the organic matter into methane, carbon dioxide and other products. The large reactors may be required because of the large quantity of liquid as compared to solid material that must be retained in a reactor, the hydraulic retention time.
The separation of the anaerobic process into the acidogenesis phase, the hydrolization of volatile suspended solids and the conversion of these into volatile fatty acids, and the methanogenesis phase, the conversion of the volatile fatty acids into methane and carbon dioxide, may have improved operation and performance of the process. However, the hydraulic retention time and the solid retention time associated with each reactor process may still be approximately equal thereby requiring large reactors because of overall fluid retention time.
There may have been some improvement in the anaerobic two phase digestion process to preprocess the organic matter influent introduced into the process and in the feedback of the methane phase reactor effluent to be reintroduced into the methane phase reactor. While such treatment may include stripping of carbon dioxide and hydrogen sulfide from the effluent as well as the introduction of small amounts of oxygen, the return of the effluent to the methane phase reactor may only improve methane gas production, but not significantly reduce retention times.
If hydraulic retention times can be reduced, wherein the large volume reactors may not be necessary for such fluid retention, then the cost associated with the use of large reactors to produce proportional quantities of product gasses and other effluent may be reduced to allow for an improved, economical, more efficient anaerobic two phase digestion process.